Interpretive Summary: Dormancy in underground adventitious buds (commonly referred to as crown and root buds) of the perennial weed leafy spurge helps to facilitate its escape from conventional control measures. Photoperiod and temperature are known to coordinately regulate molecular networks involved in plant growth and development in leafy spurge. To determine how these two environmental factors impact molecular networks to induce endo-dormancy in crown buds of leafy spurge, we compared the effects of ramp down in temperature and photoperiod (RDtp) vs. ramp down in temperature (RDt) alone. We found that a ramp-down in both photoperiod and temperature is needed to induce endo-dormancy development, which inhibits shoot growth from crown buds even during periods when environmental conditions might promote growth. In addition, we identified specific genes, metabolites, and metabolic pathways/networks that were altered in association with endo-dormancy development. We further showed that a growth regulator, ethylene, can induce arrested growth of vegetative shoots from crown buds in a manner that mimics growth from endo-dormant crown buds. Such information is useful to develop new strategies for manipulation of plant growth and development in perennial weeds, as well as crops.

Technical Abstract:
Leafy spurge is a model for studying well-defined phases of dormancy in underground adventitious buds (UABs) of herbaceous perennial weeds, which is a primary factor facilitating their escape from conventional control measures. A 12-week ramp down in both temperature (27°C ' 10°C) and photoperiod (16 h ' 8 h light) is required to induce a transition from para- to endo-dormancy in UABs of leafy spurge. To evaluate the effects of photoperiod and temperature on molecular networks of UABs during this transition, we compared global transcriptome data-sets obtained from leafy spurge exposed to a ramp down in both temperature and photoperiod (RDtp) vs. a ramp down in temperature (RDt) alone. Analysis of transcriptome data-sets indicated that genes associated with circadian clock, photoperiodism, flowering, and hormone responses (CCA1, COP1, HY5, MAF3, MAX2) were preferentially up-regulated in endodormant UABs. Gene-set enrichment analyses also highlighted metabolic pathways involved in endodormancy induction that were associated with ethylene, auxin, flavonoids, and carbohydrate metabolism; whereas, sub-network enrichment analyses identified hubs (CCA1, CO, FRI, miR172A, EINs, DREBs) of molecular networks associated with carbohydrate metabolism, circadian clock, flowering, and stress and hormone responses. These results helped refine existing models for the transition to endodormancy in UABs of leafy spurge, which strengthened the roles of circadian clock associated genes, DREBs, COP1-HY5, carbohydrate metabolism, and involvement of hormones (ABA, ethylene, and strigolactones). We further examined the effects of ethylene by application of 1-aminocyclopropane-1-carboxylate (ACC) to paradormant plants without a ramp down treatment. New vegetative growth from UABs of ACC-treated plants induced a dwarfed phenotype that mimicked the growth response in RDtp-induced endodormant UABs. The results of this study provide new insights into dormancy regulation suggesting a short-photoperiod treatment provides an additive cross-talk effect with temperature signals that may impact ethylene effects on AP2/ERF family members.